It is now standard procedure to perfuse the heart of a patient undergoing cardiac surgery with blood by any of a number of techniques. Most commonly, blood is supplied at essentially constant rate, the rate being adjustable in accordance with the observed condition of the patient. This type of supply procedure introduces difficulties where the patient's blood pressure may be varying as the result of beating of the heart, and attempts have been made to modify the feed rate to correlate with systolic and diastolic pressures in the vascular system.
A preferred method is to feed the blood at such a rate that the blood pressure in the aortic root or in a coronary blood vessel is held at a selected value. One difficulty which has been encountered arises from the fact that there is a pressure drop in the supply tube, the size of this pressure drop depending upon the flow rate of blood through the tube so that accurate determination of the pressure at the point of supply becomes difficult. Further difficulties arise from the fact that every possible contingency must be provided for, especially power failure. As is evident, then, a system which can supply blood in a mode consistent with the best interests of the patient, which is simple and inexpensive as well as light in weight, and which can provide protection for the patient against virtually any type of failure is greatly to be desired.